Each of the three parties has something the others must not see, and any arrangement ignoring that will be refused by whoever has most to lose.
What the supplier accepted is between them and the financier. The buyer has no business knowing their supplier discounted at all.
Who they sell to and in what volume is the core of their business, and exactly what a competitor would want.
Not the invoice, not the supplier, not the fact that financing was sought. There is no list to browse.
We keep the system running and take no part in what it carries.
Design stage, nothing for sale. What helps is the real mechanics: what you verify before advancing, and what the gaps are worth.